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Abstract

We explore the feasibility of single atom detection on an atom chip by using a tiny fluorescence detector mounted on the chip. Resonant fluorescence from a trapped ultracold atom will be collected with a miniature aspheric lens and taken out of a vacuum chamber through a fiber. During detection, the atom can be held at the focus of the detector with a dipole trapping beam introduced through the same fiber. We have experimentally determined the optical performance of such a detector, taking into account effects such as stray light from the dipole trapping beam and chromatic aberration. The collection efficiency for isotropically emitted radiation is experimentally obtained to be 2.5%. From this, it is estimated that the fluorescence emitted from a single Rb atom will produce a photon count rate of 4.7×104 Hz, which is much larger than the shot noise limited background fluctuations.

Figures (3)

Sketch of the setup for single atom observation on a microchip. The detector composed of an aspheric lens and a single-mode fiber is fixed on the chip using a triangular block. The fiber transports both the 780 nm fluorescence light and the 830 nm light used to trap the atom during detection. 780 nm fluorescence is spectroscopically separated from 830 nm stray light and detected with an APD.

(a). Experimental setup for measurement of chromatic aberration by using a transversely scanned knife edge. 780 nm and 830 nm beams are coupled into the same fiber, so that their output can be measured alternatively without realignment. (Only one of the beams is active at a given time.) (b) Waist radius measurement for d=5 mm. Each point in Fig. 2(c) is deduced from one such measurement. (c) Chromatic aberration (distance between the foci of the two wavelengths) (black squares) and Rayleigh length of 780 nm light (red circles) as a function of the distance d. For all the distances, the chromatic aberration is less than the Rayleigh length.

Black squares and red circles show the coupling efficiency of 780 nm-light η780 and collection efficiency α as a function of the distance d. Both the coupling efficiency and the collection efficiency are optimized at d=5 mm. Their maximum values are 0.59 and 0.025, respectively.